Lubricating oils



Patented Dec. 26, 1944 lLUBRlCATING oILs Cyril Henry Barton and Thomas Picton Hughes,

London, England, assignors to Shell Development Company, San Francisco, Calif.

No Drawing. Application August 24, 1942, Serial No. 455,870. In Great Britain August 7, 1941 1 Claim.

reduction and transmission gears and in internal combustion engines, such as aero engines and compression ignition or Diesel engine, in which a dry-sump lubrication system is employed. In such engines the lubricating oil is supplied by a pump to the engine. After use the oil drains to a sump and is withdrawn from the engine by a scavenge pump and returned to the oil reservoir for re-delivery to the engine by the feed pump. The scavenge pump generally has a capacity for handling several times as much oil as it actually withdraws from the engine sump and hence it sucks" several volumes of air with each volume of oil. The resultant mixing of oil and air'in the pump causes the oil to be returned to the reservoir largely in the form of a froth. If the froth does not break rapidly in the tank it the feed pump with the result that the engine receives more air than oil and the bearings are, in effect, starved of lubricant. Another objectionable result of frothing is that it may lead to loss of oil through the vents of the oil reservoir since the tank may be unable to contain the great volume of foam which is much larger than that of the lubricant itself.

It will be understood therefore that great benefit may be obtained from the use of an antifoaming agent dissolved in the lubricating oil, especially when the agent has no adverse effect on the lubricant and engine and manifests itself only by its action in causing rapid dispersal of the foam. We have found that a number of substances behave as anti-foaming agents and they all belong to the general group of chemical substances knownas soaps or alkali metal salt of alkyl sulphates. All substances belonging to these groups are, however, not active in reducing froths.

Accordingly, the present invention provides lubricating oil compositions comprising lubricating oils and 0.01 to 0.10% of the calcium soaps of wool oleins, or 0.1 to 0.5% of sodium alkyl esters of sulphuric acid in which the alkyl group contains more than ten carbon atoms.

The compositions according to the present invention preferably contain a trace of water since may be taken up and supplied to the engine by this enhances the effectiveness of the anti-foaming agents employed.

The calcium soaps of wool olein may be prepared by the following method from the material known commercially as "wool olein. which is manufactured from crude wool grease. 1 part by weight of wool olein is mixed with 3 parts by weight of mineral heavy machine oil, having a viscosity from 150 to 300 seconds Redwood 1 at 140 F. The mixture is heated to C. Slaked lime is added to give 10% in excess of that requgred'to neutralize the wool olein (the proportion of lime for this purpose is generally 11-12% of the wool olein). The lime is added slowly with constant stirring over a period of about 15 minutes and stirring is continued until the mixture is alkaline to phenolphthalein. The final product contains 25% of the calcium soaps of wool olein. It may be dissolved readily in any lubricating oil by mixing in the required proportion at about 50 to 60 C.

The relative stability of oil foams is compared in the laboratory by blowing filtered air through the oil until a froth of a certain heighti formed. The rate at which the froth collapses whenthe air-stream is cut oil is measured. The apparatus and details of the test are as follows:

An air-stream, after passing through cotton- Wool to remove any oil carried over from the electrically driven blower, enters a'Winchester quart bottle serving as a reservoir and pressure stabilizer and then passes to the frothing apparatus. From the connection'between the reservoir and the frothing apparatus hereinafter described, two side-pieces leadofi to a gas overflow and a release valve respectively. The gas overflow is so arranged and calibrated that, by adju ting a screw clip on the release valve, the air-stream can be maintained at 15 to 40 cms. water pressure;

The foaming proper takes place in a frothing apparatus consisting of a 250 ccs. graduated cylinder (3.8 cms. internal diameter) clamped vertically in a 3 litre beaker filled with a white oil maintained at 60i1 C. allowed to rest on the bottom of the beaker as. owing to its thick glass base, there would be a danger of the cylinder cracking.)

A gas distributor having a sintered glass plate from which the air emerges is placed in the cylinder and allowed to stand on the bottom in a horizontal position.

A centimetre scale (0 to' 10 cms.) is etched on the cylinder wall with the zero mark at such a height that, when the distributor is in position (The cylinder is not (and not containing oil), 50 cos. of oil lie above the sintered glassplate of the distributor and reach to the zero mark.

The cylinder and distributor are cleaned after each test first with acid and then with 60-80 C. petroleum ether and diethyl ether and the cylinder is placed in the bath. The requisite amount of oil at 60 C.-in this case 52 ccs.- is poured in and after allowing the temperature to become stabilised, the blower is started and air is conducted through the distributor for a few minutes before lowering it into the oil. The stopcock is then adjusted so that an air current at 40 cms.

water pressure is passed through and this is maintained until the head of foam passes the 10 cms. mark. Then the pressure is reduced to 15 cms. Water pressure, which is sufficient to preventthe oil entering the distributor without any blowing action taking place.

When the foam begins to break a stopcock is started as the surface of the foam passes below the 10 cms. mark, and the'times of passin the 7-5-43-2-1.5-1-0.5 0 cm. marks are recorded. The 0 cm. time is considered to be the moment when the foam bubbles on the oil surface first begin to break leaving a small area of clear oil, though there may still be foam on the sides of the cylinder, which may persist for a considerable time.

Using the above apparatus it has been found that minera1 lubricants produce a foam which persists for periods varying from about 5 to 20 minutes, according to the viscosity and origin of the oil; The addition to the oil of 0.01% by weight of the calcium soap of wool olein or 0.1% of a sodium alkyl ester of sulphuric acid causes rapid subsidence of the foam so that after three minutes from the moment when the air flow is topped, the height of the foam drops from 10 cms. to 1 cm.

On the other hand the addition of wool grease neutralised by lime tends to increase the foam forming properties of the oil.

We claim:

Lubricating oil composition comprising lubricating oil and 0.01 to 0.10% by weight of calcium soap of wool olein.

CYRIL HENRY BARTON. THOMAS PICTON HUGHES. 

